A secondary battery has been popularly used as a power source for electronic equipment such as a mobile phone or IT equipment, in addition to an application where a primary battery is replaced with a secondary battery. Particularly, a nonaqueous electrolyte secondary battery represented by a lithium ion secondary battery possesses high energy density and hence, the application of the nonaqueous electrolyte secondary battery to electrical equipment such as an electric vehicle has been in progress. Aiming at the outputting of high energy and the acquisition of large capacity, the secondary batteries have been used in general in the form of an energy storage module (power source module) which includes a plurality of secondary batteries.
An energy storage module has a cell stack formed by arranging a plurality of secondary batteries (energy storage devices) in a row, and the energy storage module is housed in a housing. By housing the energy storage module in the housing, the energy storage module is used as an energy storage pack (hereafter also referred to as “energy storage apparatus”) which is portable and is also mountable on an external load (see FIGS. 1, 2 and the like of JP 2013-168355A, for example).